The aim of this project is to provide a biochemical understanding of the regulation of intracellular calcium in the initiation of muscle contraction. The transverse (T)-tubule is viewed as a mediator between membrane depolarization and calcium release from the sarcoplasmic reticulum (SR); but the mechanism of this process is largely unknown. Recently, a method for isolating T-tubules, longitudinal SR and terminal cisternal (TC) vesicles had been established by the applicant and coworkers. The immediate aim is to reveal the properties of its membrane protein components and its organization in the membrane will be studied by SDS-gel electrophoresis, specific ligand bindings and interactions with cross-linking reagents. Its ion permeability and transport systems will be explored by radioisotope tracing. Also, the interaction between the T-tubules and TC will be investigated. Preliminary studies indicated that under certain conditions, the detached T-tubular vesicles will rejoin to TC vesicles forming triads again. Some specific membrane proteins may be responsible for the recognition and reattachment process. Since these proteins may play a key role in the communication between the T-tubule and the SR, attempts will be made to identify and to purify these proteins for further characterization. The anticipated procedures are the use of ion-exchange chromatography and isoelectric focusing.